Cost-effective and eco-friendly manufacture of titanium components via the near-net-shape electrochemical metallisation process

Titanium is an outstanding material, due to its unique set of properties, which is sought after in almost every industry. However, with great properties comes a great price, which for titanium is the ironic statement as it is the 9th most abundant element in the Earth’s crust. The price, instead, comes from the extraction and fabrication conventionally adopted by the industry. The extraction of titanium is currently done via the Kroll Process, which was established in 1940 and has almost reached saturation in its development and optimisation. Due to this, many novel extraction techniques have emerged, such as the FFC-Cambridge Process; an electrolytic reduction process conducted in molten salt. This process has been shown to reduce the cost associated with the production of titanium and has been intensively investigated since its development. As previously stated, the fabrication of titanium is another problematic area due to the low heat dissipation, low Young's modulus and high reactivity of titanium. Therefore, titanium is required to be treated in an inert atmosphere and when shaped the additional coolant needs to be supplied, which still does not remove the increased wear of milling tools that is common to titanium forming. These obstacles were reported to be overcome by utilising the unique solid-state transformation seen in the FFC-Cambridge Process, which results in the near-net-shaped reduction of the precursor into a metallic product. Previous studies covered the use of slip casting to shape the precursor, which reduces the versatility of the process due to the low variety of possible products. In this project for the first time, the combination of the FFC-Cambridge Process with the ceramic 3D Printing was decided to be investigated and optimised, creating a new additive manufacture technique named the Near-net-shape Electrochemical Metallisation (NEM) Process. The first step of the NEM Process was Direct Ink Writing (DIW), which allowed the viscous ink to be extruded in layers that built up the 3D structure. Optimisation of DIW for titanium dioxide printing was conducted, along with some of the modification to the mechanics of the process. The initial study on the formulation of the titanium dioxide ink was facilitated by the extrudability and rheological tests. These tests indicated that among the wide variety of inks, the one containing Polyethylene Glycol (PEG) was performing the best on a small scale. When the size of the products was increased, the inconsistency of flow became more distinct. This change was found to be caused by a complex interaction within the components of the ink at higher shear rates, which was overcome by the addition of surface lubricant. The high-quality products were achieved from DIW with the titanium dioxide ink that contained the following components in the weight ratio: 1 of TiO2, 0.9 of 10% aqueous solution of PEG and 0.1 of mixed oil. The next step of the NEM process focuses on the electrochemical metallisation of these titanium dioxide components via the constant voltage electrolysis in 900 oC CaCl2, which resulted in a noticeable deformation of the titanium product. It is important to highlight that this phenomenon has not previously been reported before and, thus, required an in-depth investigation. Following results showed the dependencies between salt temperature, pre-sintering and design with the deformation. It was noted that the temperature of the salt during the electrolysis affected the sintering of the produced titanium parts, causing products to shrink by up to 40% and dramatically deform. This, however, was found to be mitigated to some degree by the sintering of the precursors for 1 hour at 1100 oC. The resulted product had a suitable density and porosity to be successfully reduced to metallic titanium with compressive strength of 111.4 MPa and Young’s modulus of 1.39 GPa that was reported to be similar to the conventionally produced titanium foams with similar porosity (around 50%). In addition to that, the oxygen content was recorded to be as low as 1000 PPM, another sign of the successful reduction to metallic titanium, but it was found to be depended on the geometry of the product. Moreover, some attention was given to deformations that were caused by the design flaws, which unfortunately were not possible to predict and could be eliminated only by the iteration in the design. Finally, a lot of work was done to evaluate the feasibility of the NEM Process in both cost and environmental aspects. Conducted cost evaluation demonstrated an incredible cost reduction compared to conventional additive manufacture technique, measuring a cost reduction of up to 4 times. In addition to that, the cost breakdown was found to be heavily dependent on the labour cost, which reached 56% of the cost of one tooth implant. The environmental impact of the NEM Process was assessed on the gate-to-gate principle using the Life Cycle Assessment (LCA) following the established international standard. This evaluation was done in two parts, first was the investigation of the main contributors towards the environmental impact, pointing out two major contributors that were argon consumption and electrode materials. Due to this a few possible optimisations to the process were proposed such as ``smart'' argon consumption and the need for reusable electrode materials. Implementing both showed a possible reduction of the overall environmental impact of 10-15%. The second part of the LCA was comparative analysis where the NEM Process was compared against the commercially used Kroll - Electron Beam Melting (EBM) process. This showed that the overall impact of the NEM Process was lower than the Kroll - EBM Process by around 67%. Additionally, acquired data were also applied to the legislations that mainly monitor NOx, SO2, PM2.5 and CO2, the emission of which was found to be more than 70% lower for the NEM Process. This project resulted in the development of a feasible and green manufacturing route of titanium components in a safe and relatively fast way. Along with that numerous new ideas and discoveries were made that deserve further research and have the potential to improve our quality of life

Environmental assessment of the near-net-shape electrochemical metallisation process and the Kroll-electron beam melting process for titanium manufacture

The enforcement of environmental policies, in recent years, has become one of the major driving forces for industrial upgrading. Therefore, this study is focused on the evaluation of the environmental impact of a newly proposed titanium additive manufacturing process, including its in-depth comparison with the conventional method. This new method, referred to as Near-net-shape Electrochemical Metallisation, is based on the in-situ metallisation (via the FFC-Cambridge Process) of 3D-printed titanium oxide precursors (using Direct Ink Writing Process). In order to evaluate the main contributors to the environmental damage and to compare them with the conventional route for titanium manufacturing, the gate-to-gate Life Cycle Assessment has been conducted following established international standards. From this, the main contributors within the Near-net-shape Electrochemical Metallisation process were identified to be electricity and synthetic rutile, with medium impacts from argon and nickel. It was found that major impacts were challenging to be reduced without affecting the properties of the final product. However, the medium impacts can theoretically be modified, yielding potential improvements in the sustainability of the process by 10%. When compared to the conventional route (consisting of the Kroll Process, Free Fall Gas Atomisation and Electron Beam Melting), the end point results demonstrated that, by adopting the Near-net-shape Electrochemical Metallisation Process, the overall impact of titanium fabrication was dramatically reduced. Specifically, an average reduction of 68% for the ecosystem, human health and resources was observed

Development of the Fray-Farthing-Chen Cambridge Process: towards the sustainable production of titanium and its alloys

The Kroll process has been employed for titanium extraction since the 1950s. It is a labour and energy intensive multi-step semi-batch process. The post-extraction processes for making the raw titanium into alloys and products are also excessive, including multiple remelting steps. Invented in the late 1990s, the Fray-Farthing-Chen (FFC) Cambridge process extracts titanium from solid oxides at lower energy consumption via electrochemical reduction in molten salts. Its ability to produce alloys and powders, while retaining the cathode shape also promises energy and material efficient manufacturing. Focusing on titanium and its alloys, this article reviews the recent development of the FFC-Cambridge process in two aspects, (i) resource and process sustainability and (ii) advanced post-extraction processing

Rheological study and printability investigation of titania inks for direct ink writing process

Titanium dioxide is widely used in numerous industries and with the newly developed titanium manufacturing technique, referred to as the Near-net-shape Electrochemical Metallisation (NEM) Process, the rapid and precise production of titanium dioxide components is highly sought-after. This manuscript presents the rheological investigation and extrudability tests of titania inks, to establish the improved production of titanium dioxide components via Direct Ink Writing. The extrudability tests indicated that despite an unfavourable increase in viscosity during the high shear rates (dilatancy peaks), the best-performing ink had a weight ratio of 1:0.8:0.1 TiO2:H2O:PEG, and the dilatancy peaks were smoothed out with the addition of 0.1 wt ratio of oleic acid to the ink, dramatically improving the quality of the product. To further improve the green bodies a new printing approach was also introduced, removing the necessity for specialised printing bed, by printing a removable support into the green body and allowing for drying without any cracks and warping

Cost-effective and eco-friendly manufacture of titanium components via the near-net-shape electrochemical metallisation process

Titanium is an outstanding material, due to its unique set of properties, which is sought after in almost every industry. However, with great properties comes a great price, which for titanium is the ironic statement as it is the 9th most abundant element in the Earth’s crust. The price, instead, comes from the extraction and fabrication conventionally adopted by the industry. The extraction of titanium is currently done via the Kroll Process, which was established in 1940 and has almost reached saturation in its development and optimisation. Due to this, many novel extraction techniques have emerged, such as the FFC-Cambridge Process; an electrolytic reduction process conducted in molten salt. This process has been shown to reduce the cost associated with the production of titanium and has been intensively investigated since its development. As previously stated, the fabrication of titanium is another problematic area due to the low heat dissipation, low Young's modulus and high reactivity of titanium. Therefore, titanium is required to be treated in an inert atmosphere and when shaped the additional coolant needs to be supplied, which still does not remove the increased wear of milling tools that is common to titanium forming. These obstacles were reported to be overcome by utilising the unique solid-state transformation seen in the FFC-Cambridge Process, which results in the near-net-shaped reduction of the precursor into a metallic product. Previous studies covered the use of slip casting to shape the precursor, which reduces the versatility of the process due to the low variety of possible products. In this project for the first time, the combination of the FFC-Cambridge Process with the ceramic 3D Printing was decided to be investigated and optimised, creating a new additive manufacture technique named the Near-net-shape Electrochemical Metallisation (NEM) Process. The first step of the NEM Process was Direct Ink Writing (DIW), which allowed the viscous ink to be extruded in layers that built up the 3D structure. Optimisation of DIW for titanium dioxide printing was conducted, along with some of the modification to the mechanics of the process. The initial study on the formulation of the titanium dioxide ink was facilitated by the extrudability and rheological tests. These tests indicated that among the wide variety of inks, the one containing Polyethylene Glycol (PEG) was performing the best on a small scale. When the size of the products was increased, the inconsistency of flow became more distinct. This change was found to be caused by a complex interaction within the components of the ink at higher shear rates, which was overcome by the addition of surface lubricant. The high-quality products were achieved from DIW with the titanium dioxide ink that contained the following components in the weight ratio: 1 of TiO2, 0.9 of 10% aqueous solution of PEG and 0.1 of mixed oil. The next step of the NEM process focuses on the electrochemical metallisation of these titanium dioxide components via the constant voltage electrolysis in 900 oC CaCl2, which resulted in a noticeable deformation of the titanium product. It is important to highlight that this phenomenon has not previously been reported before and, thus, required an in-depth investigation. Following results showed the dependencies between salt temperature, pre-sintering and design with the deformation. It was noted that the temperature of the salt during the electrolysis affected the sintering of the produced titanium parts, causing products to shrink by up to 40% and dramatically deform. This, however, was found to be mitigated to some degree by the sintering of the precursors for 1 hour at 1100 oC. The resulted product had a suitable density and porosity to be successfully reduced to metallic titanium with compressive strength of 111.4 MPa and Young’s modulus of 1.39 GPa that was reported to be similar to the conventionally produced titanium foams with similar porosity (around 50%). In addition to that, the oxygen content was recorded to be as low as 1000 PPM, another sign of the successful reduction to metallic titanium, but it was found to be depended on the geometry of the product. Moreover, some attention was given to deformations that were caused by the design flaws, which unfortunately were not possible to predict and could be eliminated only by the iteration in the design. Finally, a lot of work was done to evaluate the feasibility of the NEM Process in both cost and environmental aspects. Conducted cost evaluation demonstrated an incredible cost reduction compared to conventional additive manufacture technique, measuring a cost reduction of up to 4 times. In addition to that, the cost breakdown was found to be heavily dependent on the labour cost, which reached 56% of the cost of one tooth implant. The environmental impact of the NEM Process was assessed on the gate-to-gate principle using the Life Cycle Assessment (LCA) following the established international standard. This evaluation was done in two parts, first was the investigation of the main contributors towards the environmental impact, pointing out two major contributors that were argon consumption and electrode materials. Due to this a few possible optimisations to the process were proposed such as ``smart'' argon consumption and the need for reusable electrode materials. Implementing both showed a possible reduction of the overall environmental impact of 10-15%. The second part of the LCA was comparative analysis where the NEM Process was compared against the commercially used Kroll - Electron Beam Melting (EBM) process. This showed that the overall impact of the NEM Process was lower than the Kroll - EBM Process by around 67%. Additionally, acquired data were also applied to the legislations that mainly monitor NOx, SO2, PM2.5 and CO2, the emission of which was found to be more than 70% lower for the NEM Process. This project resulted in the development of a feasible and green manufacturing route of titanium components in a safe and relatively fast way. Along with that numerous new ideas and discoveries were made that deserve further research and have the potential to improve our quality of life

Advanced Analysis of Electroretinograms Based on Wavelet Scalogram Processing

The electroretinography (ERG) is a diagnostic test that measures the electrical activity of the retina in response to a light stimulus. The current ERG signal analysis uses four components, namely amplitude, and the latency of a-wave and b-wave. Nowadays, the international electrophysiology community established the standard for electroretinography in 2008. However, in terms of signal analysis, there were no major changes. ERG analysis is still based on a four-component evaluation. The article describes the ERG database, including the classification of signals via the advanced analysis of electroretinograms based on wavelet scalogram processing. To implement an extended analysis of the ERG, the parameters extracted from the wavelet scalogram of the signal were obtained using digital image processing and machine learning methods. Specifically, the study focused on the preprocessing of wavelet scalogram as images, and the extraction of connected components and thier evaluation. As a machine learning method, a decision tree was selected as one that incorporated feature selection. The study results show that the proposed algorithm more accurately implements the classification of adult electroretinogram signals by 19%, and pediatric signals by 20%, in comparison with the classical features of ERG. The promising use of ERG is presented using differential diagnostics, which may also be used in preclinical toxicology and experimental modeling. The problem of developing methods for electrophysiological signals analysis in ophthalmology is associated with the complex morphological structures of electrophysiological signal components

OculusGraphy: Signal Analysis of the Electroretinogram in a Rabbit Model of Endophthalmitis Using Discrete and Continuous Wavelet Transforms

Background: The electroretinogram is a clinical test used to assess the function of the photoreceptors and retinal circuits of various cells in the eye, with the recorded waveform being the result of the summated response of neural generators across the retina. Methods: The present investigation involved an analysis of the electroretinogram waveform in both the time and time–frequency domains through the utilization of the discrete wavelet transform and continuous wavelet transform techniques. The primary aim of this study was to monitor and evaluate the effects of treatment in a New Zealand rabbit model of endophthalmitis via electroretinogram waveform analysis and to compare these with normal human electroretinograms. Results: The wavelet scalograms were analyzed using various mother wavelets, including the Daubechies, Ricker, Wavelet Biorthogonal 3.1 (bior3.1), Morlet, Haar, and Gaussian wavelets. Distinctive variances were identified in the wavelet scalograms between rabbit and human electroretinograms. The wavelet scalograms in the rabbit model of endophthalmitis showed recovery with treatment in parallel with the time-domain features. Conclusions: The study compared adult, child, and rabbit electroretinogram responses using DWT and CWT, finding that adult signals had higher power than child signals, and that rabbit signals showed differences in the a-wave and b-wave depending on the type of response tested, while the Haar wavelet was found to be superior in visualizing frequency components in electrophysiological signals for following the treatment of endophthalmitis and may give additional outcome measures for the management of retinal disease